Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic systems. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), resistive random access memory (RRAM), double data rate memory (DDR), low power double data rate memory (LPDDR), phase change memory (PCM) and Flash memory.
Non-volatile memory is memory that can retain its stored data for some extended period without the application of power. Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices are commonly used in electronic systems, such as personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones, and removable memory modules, and the uses for Flash memory continue to expand.
Flash memory typically utilizes one of two basic architectures known as NOR Flash and NAND Flash. The designation is derived from the logic used to read the devices. Typically, an array of memory cells for NAND flash memory devices is arranged such that memory cells of a string are connected together in series, source to drain.
Flash memory typically requires a negative voltage source for performing at least a portion of sensing operations, such as read and verify operations, on selected memory cells. These negative voltage sources typically comprise negative voltage charge pumps and tend to consume undesirable amounts of physical space (e.g., real estate) in memory devices. Various methods have been used to attempt to perform negative sensing operations in memory cells without having to rely on circuitry such as the real-estate intensive circuitry of negative charge pumps. However, these methods have their limitations as to the magnitude of negative sensing operations which can be performed in memory devices while still maintaining a desired level of reliability of the sensing operations.
For the reasons stated above, and for other reasons which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for expanding negative voltage sensing ranges while mitigating the amount of real estate consumed by support circuitry for performing such sensing operations and maintaining a desired level of reliability in sensing operations performed in memory devices.